Gay is genetic disorder. It is called Gay Spectrum Disorder (GSD).

Mild Gay - a person who like to look at same sex but does not want to have sex with them. Only admiring.
Medium Gay - also known as Bisexual. Mostly already married with different sex but also have same sex outside marriage. We can see this in the news where a married guy caught with having sex with another guy. Also some are gay and then go back to straight. This are just Bisexual.
Severe Gay - only into having sex with same sex

Autism Spectrum Disorder is genetic. Gay Spectrum Disorder also genetic disorder. There's no cure but therapy can be done only to suppress but it will definitely still there.

Medium gay are known to spread gay Gene. It is better for any gay or mid gay not to married so that gay Gene can be stopped from spreading

In the current news that both two brothers are gay and LGBT. This prove gay is genetic.

https://en.m.wikipedia.org/wiki/Human_sexuality_spectrum

https://en.m.wikipedia.org/wiki/Kinsey_scale

No. Sexual is a Spectrum ranging from mild to severe because it's genetic disorder.
It has nothing to do with autism. Autism is a example of genetic disorder which is also Spectrum.

Normally a being are usually want to reproductive to ensure survival of the species. In this context if same sex means it endangered the species survival and hence you can call it defective.